The present invention relates to an air conditioner equipped with an electric compressor and an electric compressor driving device.
A conventional electric compressor driving device used in a car is described hereinafter with reference to drawings. FIG. 15(a) shows a perspective view illustrating an appearance of an electric compressor driving device. Case 24 made of metal has a waterproof construction and accommodates the device. Coupling-line output port 47 which has also a waterproof structure and is mounted to case 24 passes coupling line 55 therethrough. Coupling line 55 includes two wires coupled to a battery, e.g., a direct-current (DC) power supply of approximately 300V, three wires coupled to an electric compressor, two wires coupled to a 12V power supply, and three wires carrying controlling signals and coupled to an air-conditioner controller.
In case 24, an inverter circuit converting a current from the battery into an alternate-current (AC) current is located. This inverter circuit generates heat due to DC/AC converting loss. This heat dissipates into cooling water running through water-cooling tube 56 mounted to case 24. The heat dissipation is not limited to the water cooling method, but an air cooling method can be used.
The above construction allows the electric compressor driving device to be placed in a car with few restrictions, so that the driving device can be disposed at a place away from the power supply, the battery.
FIG. 15(b) illustrates the inside of case 24 of the electric compressor driving device. Circuit board 57 having electric components mounted thereon and electrolytic capacitor 41 are located in case 24. Capacitor 41 is generally used as a power-current smoothing capacitor for smoothing the current supplied from the battery to the inverter circuit. An outline of the appearance is shown as line 53.
FIG. 16 shows a perspective view illustrating circuit board 57 shown in FIG. 15(b) and its related components. Circuit board 57 is coupled to an inverter circuit 54 as an inverter block which generates a heat greater than other components, so that inverter circuit 54 is mounted to a cooling structure related to water-cooling tube 56.
FIG. 17 shows a circuit diagram of the electric compressor driving device.
As shown in the drawing, battery 1 is coupled to compressor driving device 5 as a power supply through current-carrying device 2. Compressor driving device 5 includes inverter circuit 9 and electrolytic capacitor 41 for smoothing the current supplied from battery 1 to inverter circuit 9.
Inverter circuit 9 is coupled to a load, i.e., electric compressor 23. Current-carrying device 2 charges electrolytic capacitor 41 through charging resistor 10 up to a voltage of battery 1, and then closes main relay 11 for passing the current from battery 1 to inverter circuit 9. Current-carrying device 2 may be built in compressor driving device 5.
A voltage supplied from battery 1 to compressor driving device 5 is divided by upper bleeder resistor 13 and lower bleeder resistor 14, is insulated by voltage detector 16, and is then fed into inverter controlling microprocessor 19. The current passing through inverter circuit 9 is detected by current sensor 15, is insulated by current detector 17, and is fed into inverter controlling microprocessor 19.
Air-conditioner controller 21 calculates a capacity (such as a rotation speed) of compressor 23 necessary for an air-conditioner, and the capacity is input to microprocessor 19 via communication circuit 20.
Inverter controlling microprocessor 19 sends signals to gate driver 18 based on at least the inputs, thereby activating switching elements of inverter circuit 9 for driving compressor 23.
Gate driver 18 electrically insulates inverter circuit 9 from microprocessor 19. Inverter controlling microprocessor 19 receives sequential temperature data supplied from a thermistor temperature sensor of compressor 23. Switching power supply 12 produces a power for gate driver 18 and others. Current sensor 15 includes a current-carrying coil having an inductance component. This coil produces magnetic field detected by a Hall element, so that a current is determined.
This is not shown in the drawings, but a traction motor driving device is coupled to compressor driving device 5 in parallel, and current-carrying device 2 works similarly on a current-smoothing capacitor and an inverter circuit both equipped to the traction motor driving device.
12V power supply 22 is used as a power supply mainly for inverter controlling microprocessor 19 and communication circuit 20. 12V power supply 22 is also used as a power supply for many electric devices, such as air-conditioner controller 21, audio equipment, and a navigation system. 12V power supply 22 is electrically insulated from battery 1; and is however powered from battery 1 via a DC converter (not shown).
FIG. 18(a) shows a current flowing into inverter circuit 9, and FIG. 18(b) shows a current flowing into compressor driving device 5.
The waveform of the current flowing into inverter circuit 9 is like a rectangular wave. The waveform of the current flowing into compressor driving device 5 includes a constant current although having ripples due to the current flowing into inverter circuit 9 smoothed by electrolytic capacitor 41. Actual waveforms are more complicated, and FIG. 18 shows just outlines. As shown in FIG. 18(c), a DC voltage of battery 1 is applied to inverter circuit 9.
FIG. 19 is a schematic diagram of electric compressor 23 shown in FIG. 17. Compressor 23 includes metallic case 8 accommodating compressing mechanism 4 and motor 7. Refrigerant is sucked from intake 45, and motor 7 drives compressing mechanism 4 (a scroll compressing mechanism), so that the refrigerant is compressed.
The compressed refrigerant cools motor 7 before being discharged from outlet 46. Terminal 27 coupled to a winding of motor 7 in compressor 23 is connected to compressor driving device 5 shown in FIG. 17.
Electrolytic capacitor 41 discussed above has a large size to increase the size of the compressor driving device and to make the driving device heavy. Electrolytic capacitor 41 is vulnerable to vibrations and heat, thus preventing the compressor driving device from having an improved vibration proof and heat resistance.
A vehicle having a limited space, such as a compact electric vehicle and a hybrid electric vehicle, requires small components mounted in the vehicle. Further, the hybrid electric vehicle has a smaller space since having a space for an engine. Thus, no electrolytic capacitor 4 be mounted in the vehicle is proposed, but the following problems occur in this case.
The current supplied from battery 1 to inverter circuit 9 would not be smoothed without electrolytic capacitor 41. Then, the current of rectangular waveform passing through a power supply lead wire radiates electromagnetic-wave noises. As a result, a surge voltage is generated in the power supply lead wire, thereby damaging the circuit of compressor driving device 5.
FIG. 20 shows a circuit diagram in which electrolytic capacitor 41 is excluded (detailed structure is omitted). The case and junction connectors lengthen the power supply lead wire, so that a large and unstable inductance component 58 is generated in the lead wire.
Since the current is not smoothed by electrolytic capacitor 41 shown in FIG. 17, the current shown in FIG. 21(a) and flowing into inverter circuit 9 passes through the power supply lead wire. This current passes through inductance component 58, so that surge occurs as shown in FIG. 21(c) when the current is turned off.
This surge has a high voltage and may damage inverter circuit 9. Electrolytic capacitor 41 shortens the path for the current flowing into inverter circuit 9 just between capacitor 41 and circuit 9, so that the inductance between capacitor 41 and circuit 9 is small enough not to generate surge as shown in FIG. 18(c).
The current shown in FIG. 21(b) has a high frequency component, and the power supply lead wire radiates electromagnetic wave noises when this current passing through the wire.
The present invention addresses the foregoing problems, and aims to provide an air-conditioner equipped with a reliable electric compressor driving device which has a small size and light weight and does not generate electromagnetic noises or a surge voltage.
In order to solve the foregoing problems, an air conditioner according to the present invention includes a direct-current (DC) power supply, an electric compressor, and an electric compressor driving device that converts the current supplied from the DC power supply into an alternate-current (AC) current for driving the compressor. A center conductor and an outer conductor of a shield cable is used for feeding a current from the DC power supply to the electric compressor driving device.
This configuration cancels a magnetic field produced by a current flowing through the center conductor of shield cable and another magnetic field produced by a current flowing through the outer conductor since the center conductor and the outer conductor share the center axis.
Therefore, the cable has an inductance of substantially zero, thus allowing the driving device to suppressing a surge voltage and a radiated electromagnetic wave without an electrolytic capacitor.